As set forth in the commonly assigned U.S. Pat. No. 5,209,410 in the names of Wichmann, et al., the applications in which conductive, flowable materials are to be relatively uniformly applied onto a predetermined target are numerous, varied and constantly growing. While conventional spraying or coating techniques, dipping, wiping, soaking, and other applications and procedures have been implemented with varying degrees of acceptability in the industry, increased control of reliability and efficiency of the quality and the coverage of dispensing systems continues to be a driving force for continued development in this industry.
For example, it has been observed that nozzles made in accordance with the teachings of various dispensing nozzles and devices heretofore available (e.g., U.S. Pat. No. 4,749,125, Escallon et al.), can encounter problems in providing an application spray of predetermined, uniform consistency for dispensing materials at a predetermined coverage rate. The lack of ability to carefully control the volume of material coated onto a predetermined target area, and lack of control of the resulting uniformity in such applications has been successfully addressed by the electrostatic dispensing nozzle assembly disclosed in the above noted Wichmann et al. patent. The disclosure of the Wichmann et al. patent is hereby incorporated herein by reference. Particularly, the Wichmann, et al. nozzle assembly provides a device for electrostatically dispensing a flowable material onto a target at a predetermined application rate, and further enables enhanced control of the dispensing operations by providing a plurality of substantially hydraulically independent distribution chambers and attachment of each chamber to a source of flowable material. By selective supply of the flowable material to the individual chambers, critical control, uniformity, adaptability, and consistency of fluid distribution is conveniently provided without sacrificing performance or set-up time, and without a requirement for changes of equipment or structure. The pressure of the flowable material in the Wichmann, et al. dispensing nozzle assembly is maintained at a relatively low value, as the substantially delta-shaped chambers facilitate proper distribution of fluid within the nozzle without requiring higher pressures.
While the use of delta-shaped chambers has been found to be effective in providing substantially uniform flow of material within electrostatic nozzles for distribution across the width of the outlet opening of the nozzle, in some applications where uniformity of distribution across the width of the nozzle is critical, even further control of uniformity and distribution rate is desirable. For example, where tolerances of material application rates (e.g. thickness of distributed fluid) is relatively small (e.g. within 0.1-2 mils), even the most accurate and reliable nozzles heretofore available were not always dependable. Materials from which the nozzles have been produced limited the control which could be achieved by tight manufacturing procedures and designs, and the varying characteristics of fluids to be distributed often resulted in varying performance of nozzle application rates. Application of external modifiers, such as the modulator units contemplated in U.S. Pat. No. 5,086,973 (Escallon) can be used in some instances to attempt to minimize discrepancies among application rates and resultant distribution thicknesses and the like, but are generally cumbersome, unwieldy to set up and adjust for varying applications, and do not overcome the problems of nonuniformity and inconsistency in all cases.
Consequently, the technology heretofore available has had limitations with respect to consistency and uniformity of application rate and resulting material thickness on a predetermined target in various applications. This was especially true where application tolerances were critical and relatively tight. Prior art nozzle assemblies and related equipment could not provide dependable uniform distribution of fluid across the width of a distribution nozzle dispensing opening with the increasingly high accuracy and uniformity demanded by these sophisticated application environments. As also mentioned, while the Wichmann et al. dispensing nozzle assembly provided a major advance in the adaptability and applicability of electrostatic dispensing nozzles, the present invention further improves the fluid distribution characteristics and advances the nozzle art to address these ever higher performance goals.